Latensification of photographic emulsions



United States Patent 3,005 ,7 LATENSIFICATION OF PHOTOGRAPHIC EMULS Theinvention described herein may be manufactured and used by or for theGovernment for governmental purposes without the payment of any royaltythereon.

This invention relates to a method of increasing the effective speed ofphotographic emulsion by treating the emulsion with a dilute solution ofguanidine carbonate after exposure and before development.

Several methods of increasing the useful film speed of photographicemulsions have been described in photographic literature and used inpractice. Examples of such prior methods are as follows:

The use of high speed developers or extended development time;hypersensitization or treatment before camera exposure; intensificationafter development; and latent image intensification or latensificationbetween exposure and development. Latensification may be accomplished bybathing the emulsion in a solution of certain chemicals, exposure tovapors or exposure to light. This invention relates to latensificationby bathing.

Prior methods of latensification by bathing after exposure and beforedevelopment have included certain procedural techniques which rendersuch methods unsatisfactory. According to these prior procedures, thefilm must be bathed for prolonged periods and then squeegeed and driedat normal temperatures before it can be developed in the conventionalmanner. The inconvenience of drying film at room temperature in the darkprecludes its practical utilization as a method of increasing filmspeed.

The present invention is based on the discovery that the effective speedof the photographic emulsion can be multiplied by bathing it in a dilutesolution of guanidine carbonate after exposure and before developmentfor a considerable time without producing an increased background fogeven after several minutes of immersion. After ten minutes of immersionin the guanidine carbonate solution a background fog of only about 0.06above normal is produced.

The invention wfll become more apparent from the following specificembodiments:

Example 1 for about ten minutes. The emulsion is then developed with orwithout rinsing in water in a developer for about ninety seconds, forinstance, in an Eastman Kodak de- 53,005,711! Patented Oct. 24, 1961 ice5 veloper known in the trade as D-72 having the following composition:

The film is then fixed, washed and dried.

Example 2 A commercial silver halide film, having an ASA exposure indexrating of 50 is treated as described in Example 1 using instead of a 0.5molar solution a 2 molar solution of guanidine carbonate. The film isimmersed for about one minute in this solution and then developed withor without rinsing in water for about ninety seconds at 68 F. in anIlford Developer known in the trade as ID-62 having the followingcomposition:

Warm water F.) cc 750 Sodium sulfite (Anhyd) gms .50.0 Hydroquinone do12.0 Sodium carbonate (desiccated) do 60.0 Phenidone (1-phenyl-3pyrazolidone) do .5 Potassium bromide do 2.0 Benzotriazole do .2

Water to make 1.0 liter. The film is then fixed, washed and dried.

Films treated according to the present invention showan increase inspeed up to about four times the speed of normal development in theabove-described developers. Generally it may be said that an increase inthe time of immersion in guanidine carbonate results in an increase infilm speed.

It will be obvious to those skilled in the art that variousconcentrations of the guanidine carbonate solution may be used up toabout a 5 molar solution and that the time of treating the film may bevaried up to about twenty minutes according to the differentcharacteristics of the exposed film and the effects desired.

What is claimed is:

1. A method of latensification of photographic silver I halide emulsionscomprising treating the emulsion after exposure and before developingwith an aqueous solution of guanidine carbonate whereupon the emulsionis developed in the conventional manner.

2. A method of latensification of photographic silver halide emulsionsaccording to claim 1 in which the treatment with guanidine carbonate iscontinued for a time period of between one to twenty minutes.

3. A method of latensification of photographic silver halide emulsionsaccording to claim 1 in which a 1 molar solution of guanidine carbonateis used.

4. A method of latensification of photographic silver halide emulsionsaccording to claim 1 in which a 5 molar solution of guanidine carbonateis used.

5. A method of latensification of photographic silver halide emulsionsaccording to claim 1 in which the emulsion is treated in a 2 molarsolution of guanidine carbonate for about ten minutes.

References Cited in the file of this patent UNITED STATES PATENTS Joneset a1. July 11, 1939

1. A METHOD OF LATENSIFICATION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONCOMPRISING TREATING THE EMULSION AFTER EXPOSURE AND BEFORE DEVELOPINGWITH AN AQUEOUS SOLUTION OF GUANIDINE CARBONATE WHEREUPON THE EMULSIONIS DEVELOPED IN THE CONVENTIONAL MANNER.